1. Field of the Invention
The present invention relates to a test method and apparatus for a semiconductor element such as MOS or bipolar transistor, and, more particularly, a test method and apparatus for determining breakdown strength through a destructive test.
2. Description of the Prior Art
Generally, a test method for such semiconductor element employs a one described in Japanese Patent Application Laid-Open No. 2-259585, 3-15773 or 5-180899. All of these methods measure a breakdown voltage of a semiconductor element to be tested by charging voltage generated from a variable voltage supply in a capacitor with a certain capacity, changing over the capacitor to the semiconductor, and discharging the capacitor. In this case, the variable voltage supply applies a high voltage of 1000-5000V. It is common to all test methods that breakdown strength of a semiconductor element tested by such test method is represented by breakdown voltage or dielectric breakdown voltage. These test are called as breakdown test or destructive tests.
Here, it should be taken into account that the capacity of the semiconductor element largely varies between a state as a semiconductor wafer and a state as packaged in a package, and depending on the measurement environment and measurement instrument. As well known, since relationship of Q=CV or V=Q/C is established between charge Q charged in the semiconductor element, voltage V to be applied, and the capacity C, if the capacity varies in testing, breakdown voltage representing the result of test cannot be said to indeed represent an accurate value unless the relationship with the capacity is indicated.
On the other hand, the semiconductor element is generally categorized into a MOS semiconductor device and a bipolar semiconductor device. Breakdown strength of the MOS semiconductor device is mainly determined by breakdown strength of the insulating film, while that of the bipolar semiconductor device is mainly determined by breakdown strength of PN junction. Furthermore, depending on the structure or size of the semiconductor device, in many cases, the breakdown strength of the insulating film of MOS semiconductor device is represented by breakdown strength when charge in a capacitor of 1-10 pF is discharged, while the breakdown strength of PN junction is represented by breakdown strength when charge in a capacitor of 100-1000 pF is discharged. In any case, it is necessary to vary the capacity over a wide range to determine the breakdown strength of the semiconductor element. When such variation of capacity over a wide range is taken into consideration, it is obvious that the conventional test methods cannot determine accurate breakdown strength for each semiconductor element.
An object of the present invention is to provide a test method to accurately determine semiconductor element breakdown strength.
Another object of the present invention is to provide a test method for semiconductor element which can be commonly applied to various semiconductor elements.
Still another object of the present invention is to provide a test apparatus for semiconductor element which can calculate breakdown strength.